Method and apparatus for managing remote unit increased power transmission during location

ABSTRACT

Remote units (113) that require locating are managed by a queue controller (180) such that the number and location of remote units (113) that are transmitting at increased power at any given time is limited. In particular, a queue controller (180) places identification information for remote units (113) requiring location onto queues (203) associated with base stations supplying reference pilots to the remote units (113). Additionally, identification (ID) information for the remote units (113) requiring location is placed onto queues (203) associated with base stations neighboring the base stations supplying the reference pilot to the remote units (113). The queues (203) operate on a first-in-first-out (FIFO) basis, that output remote unit ID at periodic intervals. Once all queues (203) have been emptied of the ID of a particular remote unit (113), location takes place for that remote unit (113).

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationsystems and, in particular, to managing increased power transmissions ofa remote unit during location.

BACKGROUND OF THE INVENTION

It is well known that a remote unit's location within a wirelesscommunication system may be determined using a trilateration method.According to such a method, distances between the remote unit andmultiple base stations are calculated based on the measurement of a timedelay of a signal traveling between the remote unit and each basestation. Such a prior-art method for calculating a remote unit'slocation is described in U.S. Pat. No. 5,508,708 "Method and Apparatusfor Location Finding in a CDMA System" by Ghosh et al. and incorporatedby reference herein. As described in U.S. Pat. No. 5,508,708, whenlocation of a remote unit is desired, the remote unit may be instructedto increase the power at which it transmits to ensure that a sufficientamount of base stations are able to decode the remote unit'stransmission.

Although increasing a remote unit's transmit power will serve toincrease the number of base stations that the remote unit is incommunication with, during the time that the remote unit is transmittingat increased power levels, other remote units operating in the samegeographic area will be negatively affected since the increased transmitpower will be generating additional system interference. In a commercialsetting, where there can be many remote units requiring simultaneouslocation estimates, the simultaneous increase in transmit power for allremote units requiring location estimates can cause unacceptably highframe error rates (FERs), resulting in increased dropped call rates aswell as reducing the ability of the wireless communication system todetermine the location of the remote units. Thus a need exists for amethod and apparatus for managing the increased power transmission of aremote unit during location.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a wireless communication system inaccordance with the preferred embodiment of the present invention.

FIG. 2 is a block diagram of the queue controller of FIG. 1 inaccordance with the preferred embodiment of the present invention.

FIG. 3 illustrates operation of the queue of FIG. 2 in accordance with apreferred embodiment of the present invention.

FIG. 4 is a flow chart illustrating a preferred method of operating thequeue controller of FIG. 2.

FIG. 5 is a flow chart illustrating a method of operating the queuecontroller of FIG. 2 in accordance with the alternate embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Stated generally, remote units that require locating are managed by aqueue controller such that the number and location of remote units thatare transmitting at increased power at any given time is limited. Inparticular, a queue controller places identification information forremote units requiring location onto queues associated with basestations supplying reference pilots to the remote units. Additionally,identification information for the remote units requiring location isplaced onto queues associated with base stations neighboring the basestations supplying the reference pilot to the remote units. The queuesoperate on a first-in-first-out (FIFO) basis, that output a remote unitidentification at periodic intervals. Once all queues have been emptiedof the identification of a particular remote unit, location takes placefor that remote unit.

The present invention encompasses a method for locating a remote unit.The method comprises the steps of determining a first base station and asecond base station currently serving the remote unit and placingidentification information regarding the remote unit onto a first bufferassociated with the first base station. Identification informationregarding the remote unit is also placed onto a second buffer associatedwith the second base station. The identification information is removedfrom the first buffer at a first time and from the second buffer at asecond time. Finally, the remote unit is located only after informationregarding the remote unit has been removed from the first and the secondbuffers.

An alternate embodiment of the present invention encompasses a methodfor managing a location estimation of a first remote and a second remoteunit. The method comprises the steps of placing identificationinformation regarding the first and the second remote unit onto a bufferand removing the identification information regarding the first remoteunit from the buffer. After the identification information regarding thefirst remote unit is removed from the buffer, the first remote unit islocated and the buffer is locked for a predetermined amount of time sothat the identification information regarding the second remote unitcannot be removed from the buffer until the predetermined amount of timehas passed. After the predetermined amount of time has passed theidentification information regarding the second remote unit is removedfrom the buffer and the second remote unit is located.

Yet another embodiment of the present invention encompasses a method forlocating a remote unit. The method comprises the steps of determining afirst base station and a second base station currently serving theremote unit and determining if locating the remote unit will negativelyaffect remote units served by the second base station. Informationregarding the remote unit is placed onto a first buffer associated withthe first base station. If it is determined that locating the remoteunit will negatively affect remote units served by the second basestation then identification information regarding the remote unit isplaced onto a second buffer associated with the second base station.Next, the identification information is removed from the first buffer ata first time and only removed from the second buffer if locating theremote unit will negatively affect remote units served by the secondbase station. Finally the remote unit is located after identificationinformation regarding the remote unit does not exist on the first andthe second buffer.

A final embodiment of the present invention encompasses an apparatuscomprising a controller for determining a first base station and asecond base station currently serving a remote unit, a first bufferassociated with the first base station, a second buffer associated withthe second base station, and a timer for removing identificationinformation from the first buffer at a first time and removingidentification information from the second buffer at a second time.Finally locating equipment is provided coupled to the first and thesecond buffers.

FIG. 1 is a block diagram showing wireless communication system 100 inaccordance with the preferred embodiment of the present invention.Wireless communication system 100 is preferably a cellular communicationsystem that utilizes a Code Division Multiple Access (CDMA) systemprotocol, however, in alternate embodiments of the present inventioncommunication system 100 may utilize any analog or digital systemprotocol such as, but not limited to, the Advanced Mobile Phone Service(AMPS) protocol, the Global System for Mobile Communications (GSM)protocol, the Personal Digital Cellular (PDC) protocol, or the UnitedStates Digital Cellular (USDC) protocol. Communication system 100comprises remote unit 113, wireless infrastructure equipment, includingauxiliary base station 156, Centralized Base Station Controller (CBSC)160, Mobile Switching Center (MSC) 165, Home Location Register (HLR)166, and base station 101. Base station 101 has common RF front end 105which feeds independent rake inputs 110, 120, and 130. A communicationsystem utilizing the CDMA system protocol is described in detail inCellular System Remote unit-Base Station Compatibility Standard of theElectronic Industry Association/Telecommunications Industry AssociationInterim Standard 95 (IS-95-A) which is incorporated by reference herein.(EIA/TIA can be contacted at 2001 Pennsylvania Ave. NW Washington D.C.20006).

Operation of Communication system 100 in accordance with the preferredembodiment of the present invention occurs as follows: To initiate alocation request, a command is originated at a regional entity such asMSC 165, operations center 170, or perhaps within a connected networksuch as Public Switched Telephone Network (PSTN) 175. The locationrequest, which includes identification information on the remote unitthat is to be located enters HLR 166 where it is processed to determinethe currently serving base station. Once the currently serving basestation is known, the location request is passed to queue controller180. Although in the preferred embodiment of the present invention HLR166 passes the location request to queue controller 180, in alternateembodiments of the present invention the queue controller may receivethe location request along with the remote unit ID and serving basestation from any of a number of different network elements depending onthe implementation architecture of the system. In the preferredembodiment of the present invention, queue controller 180 manages thenumber and location of all location requests such that the number andlocation of remote units that are transmitting at increased power at anygiven time is limited. In particular, queue controller 180 determines anappropriate time to increase transmit power for each remote unitrequiring location such that system interference is reduced by limitingthe simultaneous increase in transmit power for multiple remote unitsrequiring location. (Further details regarding operation of queuecontroller 180 will be discussed below). By limiting the number ofremote units simultaneously transmitting at increased power levels andthereby reducing system interference, unacceptably high system frameerasure rates can be reduced, resulting in decreased dropped call rates.In addition, interference between multiple remote units requiringlocation is also reduced, resulting in an increased ability toaccurately determine the location of the remote units.

Continuing, at an appropriate time, the location request is passed fromqueue controller 180 to the base station providing remote unit 113 witha reference pilot (reference-pilot base station) and those base stationsneighboring the reference-pilot base station (the group of base stationscomprising the reference-pilot base station and base stationsneighboring the reference-pilot base station hereinafter is referred toas the group of serving base stations), where processor 150 of basestation 101 (and similar processors of other serving base stations)calculate a time delay of a signal traveling between the remote unit andeach base station. This may be accomplished as described in U.S. Pat.No. 5,508,708 by all bases determining the leading edge rise time of aspecified group of PN chips, for example by determining the rise timefor each 64th chip (i.e., PN sequence number 0, 64, 128, etc.) for apredetermined number of chips, or may be accomplished via other locationmethods (e.g., as described in U.S. Pat. No. 5,583,517 "Multi-PathResistant Frequency-Hopped Spread Spectrum Mobile Location system", oras described in U.S. Pat. No. 3,886,554 "Method and Apparatus forImproving the Accuracy of a Vehicle Location System"). Locationinformation is then forwarded by each base station 101, along with itsbase station identification, to locating equipment such as locationsearcher 161 of BSC 160, or location searcher 167 of HLR 166, etc.,where remote unit location is determined Thus, the distances between theremote unit and multiple base stations are calculated based on themeasurement of a time delay of a signal traveling between the remoteunit and each base station.

FIG. 2 is a block diagram showing queue controller 180 of FIG. 1 inaccordance with the preferred embodiment of the present invention. Queuecontroller 180 comprises controller 201, database 207, task manager 209,and multiple queues 203 each having an associated timer 205. In thepreferred embodiment of the present invention, each base station withincommunication system 100 has an associated queue 203 and timer 205, butin an alternate embodiments of the present invention, queues 203 andtimers 205 may be distributed differently (e.g., each base stationsector within communication system 100 may have an associated queue 203and timer 205).

Operation of queue controller 180 occurs as follows: Controller 201receives a remote unit location request from HLR 166, which contains theidentification of remote unit 113 and the reference-pilot base station.Controller 201 accesses database 207 and determines all base stationsneighboring the reference-pilot base station. Once the serving stationshave been determined, identification information for remote unit 113(remote unit ID) is placed onto those queues 203 associated with eachserving base station. Additionally, task manager 209 is supplied withthe remote unit ID and a number corresponding to the number of servingbase stations. Queues 203 are similar to buffers operating on afirst-in-first-out (FIFO) basis, that output a remote unit ID atperiodic intervals. In the preferred embodiment of the presentinvention, timer 205 controls queue 203 such that queue 203 will beprevented from outputting a remote unit ID for a programmable time(based on system activity, quality of service required by a serviceprovider, and call quality measurements) after outputting a remote unitID. (Further details on queue 203 are discussed below in reference toFIG. 3).

Continuing, as discussed above, task manager 209 receives remote unit IDinformation and the number of serving base stations from controller 201.Once this information is received from controller 201, task manager 209initiates an internal counter (not shown) that is associated with remoteunit 113. In the preferred embodiment of the present invention theinternal counter is initially set to zero, and incremented by "1" forevery output of remote unit 113 ID from queues 203. When the internalcounter associated with remote unit 113 is equal to the number ofserving base stations, (i.e., the ID for remote unit 113 has beenemptied from all queues 203), task manager 209 outputs the locationrequest to all serving and neighbor base stations continuing thelocation process. Thus, operation of queue controller 180 in accordancewith the preferred embodiment of the present invention serves to limitthe number of remote units simultaneously transmitting at increasedpower levels. By limiting the number of remote units simultaneouslytransmitting at increased power levels and thereby reducing systeminterference, unacceptably high system frame erasure rates can bereduced, resulting in decreased dropped call rates.

FIG. 3 illustrates operation of queue 203 in accordance with thepreferred embodiment of the present invention. For purposes of thisillustration, operation of a single queue 203 over a period of time isshown. At time to queue 203 is empty, indicating that no remote unitsutilizing the reference pilot of, or neighboring the base stationassociated with queue 203 require location. At time t1, queue 203 hasID1 place onto it and immediately removes ID1 from queue 203 and passesID1 to task manager 209. In the preferred embodiment of the presentinvention, the removal of an ID from queue 203 initiates timer 205associated with queue 203 which "locks" queue 203 so that no other ID'scan be passed from queue 203 until timer 205 expires. In the preferredembodiment of the present invention the time that queue 203 is preventedfrom outputting another remote unit 113 ID is based on 1) the minimumtime allowed by the system (a system operator controllable parameter),2) the current traffic load in the reference-pilot base station and theneighboring base stations, 3) the system required quality of serviceparameters for the reference-pilot base station and the neighboring basestations, 4) the maximum time allowed for a remote unit location to beperformed, and 5) the maximum number of entries in the queues that theremote unit ID will be placed in. In the preferred embodiment of thepresent invention the time that queue 203 is prevented from outputtinganother remote unit 113 ID is computed by the following equation:

    T=Minimum (TM, Minimum (Tm+a*L+b*Q, TI/M)),

where Tm, a, b, and TI are parameters that are defined based on specificsystem design and the operators requirements for quality of service andoperation. In the preferred embodiment of the present invention:

Tm=Minimum Time allowed by the system in milliseconds (ms)

a is the system operator controllable scale factor for Load (in ms/unitload);

L is the computed system load;

b is the system operator controllable scale factor for Quality ofservice (in ms per Quality of Service parameter);

Q is the system operator controllable quality requirement (in units ofan operator chosen-Quality of Service parameter);

TI is the maximum amount of time to allow for a remote unit locationevent (in ms); and

M is the maximum number of entries in a queue that the remote unit IDwill be placed in.

Continuing, at time t2, ID2 (associated with a second remote unitrequiring location) is placed onto queue 203. Since the timer has notexpired at time t2, ID2 remains on queue 203. At time t3 ID3 is added toqueue 203. At time t4 timer 205 has expired and ID2 is removed fromqueue 203 and passed on to task manager 209. Timer 205 is again reset to"lock" queue 203 for the required period of time. At time t5 timer 205has again expired and ID3 is passed from queue 203 to task manager 209and timer 205 is again reset.

FIG. 4 is a flow chart illustrating a preferred method of operatingqueue controller 180 of FIG. 2. The logic flow begins at step 401 wherecontroller 201 receives a remote unit location request for remote unit113. Next, at step 405 controller 201 accesses database 207 to determinethe neighbor base stations for remote unit's 113 reference-pilot basestation. Once the serving base stations are known, controller 201supplies task manager 209 with the ID of remote unit 113 and a numbercorresponding to the number of serving base stations (step 410) and taskmanager 209 initiates an internal counter that is associated with remoteunit 113 (step 415). As discussed above, the internal counter isinitially set to zero, and incremented by "1" for every output of remoteunit ID corresponding to remote unit 113 from queues 203.

Continuing, next at step 420 the ID for remote unit 113 is placed ontothose queues 203 associated with the serving base stations. At step 425it is determined by each queue 203 within queue controller 180 if anyqueues 203 are currently "unlocked." In other words, at step 425 eachindividual queue 203 within queue controller 180 determines whether ornot an associated timer 205 has expired, and if not the logic flowreturns to step 425. If at step 425 it is determined that a queue 203 is"unlocked" then the logic flow continues to step 430 where the "oldest"remote unit ID on the unlocked queue 203 is passed to task manager 209.As discussed above, each queue 203 acts as a FIFO buffer that, wheninstructed to release a remote unit ID, will release the remote unit IDthat has existed on queue 203 for the longest period of time.

Continuing, at step 435 timer 205 associated with unlocked queue 203 isreset and the logic flow continues to step 440 where it is determined ifthe ID of remote unit 113 was passed to task manager 209, and if not,the logic flow returns to step 425, otherwise the logic flow continuesto step 450 where the internal counter for remote unit 113 isincremented by "1." Next at step 450 task manager 209 determines if theinternal counter associated with remote unit 113 is equal to the numberof serving base stations. If the internal counter associated with remoteunit 113 is not equal to the number of serving base stations then thelogic flow returns to step 425, otherwise, the ID for remote unit 113has been cleared from all queues 203 and the logic flow continues tostep 455 where task manager 209 outputs a location request to servingbase locations for location of remote unit 113.

FIG. 5 is a flow chart illustrating a method of operating the queuecontroller 180 of FIG. 2 in accordance with an alternate embodiment ofthe present invention. In the alternate embodiment of the presentinvention, queue controller 180 determines if locating remote unit 113will negatively affect remote units served by neighbor base stations,and if not, queue controller 180 places remote unit 113 only onto thequeue corresponding to the reference-pilot base station (i.e.,controller 180 does not place remote unit 113 onto queues correspondingto neighbor base stations). The logic flow begins at step 501 wherecontroller 201 receives a remote unit location request for remote unit113. Next, at step 505 controller 201 accesses database 207 to determinethe neighbor base stations for remote unit's 113 reference-pilot basestation. Once the serving base stations are known, controller 201determines if remote unit 113 will be potential interferer with aneighbor base station if transmit power is increased (step 506). In thealternate embodiment of the present invention, controller 201 determinesif remote unit 113 will be a potential interferer by accessing thereference-pilot base station and determining a distance from thereference-pilot base station to remote unit 113. In the alternateembodiment, round-trip delay for a signal transmitted between remoteunit 113 and the reference-pilot base station is utilized in calculatingthe distance between remote unit 113 and the reference-pilot basestation.

Each base station within communication system 100 has an associateddistance threshold, beyond which, a remote unit isdetermined to be apotential interferer to remote units served by other base stations. Inthe alternate embodiment of the present invention the threshold iscalculated via the following equation:

Distance₋₋ Threshold=A*R

where,

Distance₁₃ Threshold is the maximum distance a remote unit can be fromthe base station before the queue controller determines the remote unitwill affect neighboring base stations;

R is the engineered coverage radius of the base station; and

A is the system operator controllable scale factor (0%-100%).

If the distance between the reference-pilot base station and remote unit113 is below a threshold, then remote unit 113 will not be a potentialinterferer.

Continuing, if at step 506 it is determined that remote unit 113 willnot be a potential interferer with neighbor base stations then the logicflow continues to step 507 where task manager 209 is supplied with thenumber "1" for the number of serving base stations, and initiates aninternal counter associated with remote unit 113 (step 508). At step 509controller 201 places the ID for remote unit 113 the queue 203associated with the reference-pilot base station and the logic flowcontinues to step 525.

Returning to step 506; if controller 201 determines that remote unit 113is a potential interferer with neighbor base stations, the logic flowcontinues to step 510 where a number corresponding to the number ofserving base stations is supplied to task manager 209 and task manager209 initiates an internal counter that is associated with remote unit113 (step 515). As discussed above, the internal counter is initiallyset to zero, and incremented by "1" for every output of remote unit IDcorresponding to remote unit 113 from queues 203.

Continuing, next at step 520 the ID for remote unit 113 is placed ontothose queues 203 associated with the serving base stations. At step 525it is determined by each queue 203 within queue controller 180 if anyqueues 203 are currently "unlocked." In other words, at step 525 eachindividual queue 203 within queue controller 180 determines whether ornot an associated timer 205 has expired, and if not the logic flowreturns to step 525. If at step 525 it is determined that a queue 203 is"unlocked" then the logic flow continues to step 530 where the "oldest"remote unit ID on the unlocked queue 203 is passed to task manager 209.As discussed above, each queue 203 acts as a FIFO buffer that, wheninstructed to release a remote unit ID, will release the remote unit IDthat has existed on queue 203 for the longest period of time.

Continuing, at step 535 timer 205 associated with unlocked queue 203 isreset and the logic flow continues to step 540 where it is determined ifthe ID of remote unit 113 was passed to task manager 209, and if not,the logic flow returns to step 525, otherwise the logic flow continuesto step 550 where the internal counter for remote unit 113 isincremented by "1." Next at step 550 task manager 209 determines if theinternal counter associated with remote unit 113 is equal to the numberof serving base stations. If the internal counter associated with remoteunit 113 is not equal to the number of serving base stations then thelogic flow returns to step 525, otherwise, the ID for remote unit 113has been cleared from all queues 203 and the logic flow continues tostep 555 where task manager 209 outputs a location request to servingbase stations for location of remote unit 113.

While the invention has been particularly shown and described withreference to a particular embodiment, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention andit is intended that all such changes come within the scope of thefollowing claims.

What is claimed is:
 1. A method for locating a remote unit, the methodcomprising the steps of:(a) determining a first base station and asecond base station currently serving the remote unit; (b) placingidentification information regarding the remote unit onto a first bufferassociated with the first base station; (c) placing identificationinformation regarding the remote unit onto a second buffer associatedwith the second base station; (d) removing the identificationinformation from the first buffer at a first time; (e) removing theidentification information from the second buffer at a second time,wherein the second time does not equal the first time; and (f) locatingthe remote unit, wherein the step of locating the remote unit is basedon identification information regarding the remote unit being removedfrom the first buffer and the second buffer.
 2. The method of claim 1wherein the step of removing the identification information from thesecond buffer at the second time comprises the step of removing theidentification information from the second buffer at the second time,wherein the second time is based on a current traffic load.
 3. Themethod of claim 1 wherein the step of removing the identificationinformation from the second buffer at the second time comprises the stepof removing the identification information from the second buffer at thesecond time, wherein the second time is based on a quality of service.4. The method of claim 1 wherein the step of removing the identificationinformation from the second buffer at the second time comprises the stepof removing the identification information from the second buffer at thesecond time, wherein the second time is based on a maximum time allowedfor the step of locating the remote unit to be performed.
 5. The methodof claim 1 wherein the step of locating the remote unit comprises thestep of locating the remote unit by sending a command to the remote unitto increase a remote unit transmit power.
 6. The method of claim 1wherein the step of locating the remote unit comprises the step oflocating the remote unit via trilateration.
 7. A method for managing alocation estimation of a first remote unit and a second remote unit, themethod comprising the steps of:placing identification informationregarding the first remote unit onto a buffer; placing identificationinformation regarding the second remote unit onto the buffer; removingthe identification information regarding the first remote unit from thebuffer; locating the first remote unit, wherein the step of locating thefirst remote unit is based on the identification information regardingthe first remote unit being removed from the buffer; locking the bufferfor a predetermined amount of time so that the identificationinformation regarding the second remote unit cannot be removed from thebuffer until the predetermined amount of time has passed; removing theidentification information regarding the second remote unit from thebuffer, wherein the step of removing identification informationregarding the second remote unit occurs after the predetermined amountof time has passed; and locating the second remote unit, wherein thestep of locating the second remote unit is based on the identificationinformation regarding the second remote unit being removed from thebuffer.
 8. The method of claim 7 wherein the step of locking the bufferfor a predetermined amount of time comprises the step of locking thebuffer for a predetermined amount of time, wherein the predeterminedamount of time is based on a current traffic load.
 9. The method ofclaim 7 wherein the step of locking the buffer for a predeterminedamount of time comprises the step of locking the buffer for apredetermined amount of time, wherein the predetermined amount of timeis based on a maximum time allowed for the step of locating to beperformed.
 10. The method of claim 7 wherein the step of locking thebuffer for a predetermined amount of time comprises the step of lockingthe buffer for a predetermined amount of time, wherein the predeterminedamount of time is based on a quality of service.
 11. The method of claim7 wherein the step of locating the first remote unit comprises the stepof locating the first remote unit by sending a command to the firstremote unit to increase the remote unit transmit power.
 12. A method forlocating a remote unit, the method comprising the steps of:determining afirst base station and a second base station currently serving theremote unit; determining if a step of locating the remote unit willnegatively affect remote units served by the second base station;placing identification information regarding the remote unit onto afirst buffer associated with the first base station; placingidentification information regarding the remote unit onto a secondbuffer associated with the second base station only if locating theremote unit will negatively affect remote units served by the secondbase station; removing the identification information from the firstbuffer at a first time; removing the identification information from thesecond buffer at a second time only if locating the remote unit willnegatively affect remote units served by the second base station; andlocating the remote unit, wherein the step of locating the remote unitis based on identification information regarding the remote unit notexisting on the first and the second buffer.
 13. The method of claim 12wherein the step of determining if the step of locating the remote unitwill negatively affect remote units served by the second base stationcomprises a step of determining if the remote unit is beyond apredetermined distance from the first base station.
 14. The method ofclaim 12 wherein the step of removing the identification informationfrom the second buffer at the second time comprises the step of removingthe identification information from the second buffer at the secondtime, wherein the second time is based on a current traffic load. 15.The method of claim 12 wherein the step of removing the identificationinformation from the second buffer at the second time comprises the stepof removing the identification information from the second buffer at thesecond time, wherein the second time is based on a quality of service.16. The method of claim 12 wherein the step of removing theidentification information from the second buffer at the second timecomprises the step of removing the identification information from thesecond buffer at the second time, wherein the second time is based on amaximum time allowed for the step of locating the remote unit to beperformed.
 17. The method of claim 12 wherein the step of locating theremote unit comprises the step of locating the remote unit by sending acommand to the remote unit to increase a remote unit transmit power. 18.An apparatus comprising:a controller for determining a first basestation and a second base station currently serving a remote unit; afirst buffer associated with the first base station; a second bufferassociated with the second base station; a timer for removingidentification information from the first buffer at a first time andremoving identification information from the second buffer at a secondtime, wherein the second time does not equal the first time; andlocating equipment coupled to the first and the second buffers, thelocating equipment serving to locate the remote unit only afteridentification information regarding the remote unit does not exist onthe first and the second buffers.